Reinforced insulation is required for insulation between a primary side and a secondary side of a power supply device to keep the power supply device in a safe state. Reinforced insulation is single insulation that provides mechanical and electrical protection on a par with double insulation against electric shocks. The double insulation referred to here is made up of basic insulation, i.e., insulation for basic protection against electric shocks, and supplementary insulation, i.e., independent insulation added to the basic insulation to ensure protection against electric shocks if a defect arises in the basic insulation. Functional insulation, which is used to ensure proper operation of equipment, is useful for prevention of ignition and combustion. However, this insulation does not provide protection against electric shocks.
International safety standards define insulation distances needed to ensure insulation in consideration of circuit effective voltages. The defined insulation distances include spatial distance, which is a shortest distance between two conducting parts or between a conducting part and a conductive outer surface of equipment measured through air, and a creepage distance, which is a shortest distance between two conducting parts or between a conducting part and a conductive outer surface of equipment measured along a surface of an insulator.
As described in PTL 1, for example, international standards and guidelines stipulate that an insulation distance for a welding power supply with a circuit effective voltage of 400 V should be 5.5 mm or longer in spatial distance and 6.3 mm or longer in creepage distance to provide basic insulation. The standards also stipulate that insulation between an input circuit and an output circuit should constitute reinforced insulation or double insulation, and an insulation distance should be twice a basic insulation distance, i.e., a spatial distance of 11 mm or longer and a creepage distance of 12.6 mm or longer.
PTL 2 discloses a method of ensuring the expandability of a battery system that includes a plurality of series-coupled battery modules each including a plurality of battery cells. The battery modules have photo-couplers or other insulating devices that are used to communicate information about voltages and other measurements of the respective modules with an upper management device for the battery system. A housing for each battery module has an insulation sheet and a spatial distance between the housing and each of the battery cells contained inside, and thereby maintains insulation from the battery cells.